I love the black California plate with the stickers peeled back to 1969. My '67 GT500 is an original black plate California car that still had them on it when I bought it in 1982. I peeled the stickers back to '67. There was a '67 Corvette at Cars and Coffee on Eastern Avenue that also had black plates peeled back to 1967. Pretty cool to see.
Are you talking about display only plates, or plates that the car is actually registered on?
Cars from the 60’s that have been continuously registered in CA since the 60’s, would have black plates with a current year sticker, and no other year sticker. But CA has a program that allows retro-fitting the black plates onto 63-69/70 cars, and those would have two year stickers, one for the model year of the car, plus the current year. It normally would not be legal to have a CA black 60’s style plate with only the old year visible. My discussion excludes the new style black CA legacy plates.